I was having a similar problem. Found out that because of my overclocks, my northbridge was getting really hot causing instability. I turned down the settings in crysis and it became more stable but not 100%... I would say about 75% more stable. So i decided to lower my overclock from 3Ghz, to 2.5 to see what would happen.

No negative impact on performance, no superhot NB, and not a single crash.